In the treatment of leukemia, eradicating the stem cells which contribute to leukemia cell outgrowth is a necessary yet difficult task due to the quiescent nature of the stem cell and its interactions with marrow microenvironment. Hematopoietic stem cells and their leukemic counterparts interact with marrow and vascular environments in which they reside and circulate. These interactions are thought to contribute to cell survival, proliferation, apoptosis, and differentiation, but much remains to be learned about how they might be manipulated to enhance normal stem cell function and survival and to optimize elimination of abnormal hematopoietic stem cells. Understanding these interactions would therefore have implications for normal stem cell transplantation and for therapy of various types of leukemias. It has been shown that hematopoieitic stem cells roll more slowly on selectins and other substrata than do other blood elements. In this proposal, the dynamic interaction of normal and leukemic hematopoietic stem cells with selectins and other substrata will be examined. The hypothesis to be tested is that the differential rolling potential of stem cells can be exploited to influence capture, adhesion, and apoptosis in hematologic malignancy states. In order to test this hypothesis, three specific aims are proposed: In the first aim, the ability of normal and leukemic hematopoietic stem cells from blood and marrow to be captured in a microcapillary tube system based on interactions with selectins will be tested. This will utilize a design previously established to exploit differences in rolling of stem cells compared with other cell types and based on modeled hydrodynamic phenomena. A glass capillary network that promotes margination of stem cells to the vessel wall will be utilized. In the second aim, the role that the CXC chemokine, stromal derived factor-1 ? and its receptor, CXCR4 and VLA-4/VCAM-1 have on stem cell capture in both dynamic and static adhesion systems will be examined. Effects on stem cell proliferation, survival, and clonogenicity will be examined. Potential for homing and engraftment in an NOD/SCID mouse model will also be measured. In the third aim, whether normal vs. leukemic stem cells can be differentially captured in a dynamic capillary flow system will be examined. Effects that exposure to agents with specific anti-apoptotic effects for leukemic vs normal progenitor cells have on cell-substrata interactions will also be explored. Agents such as TNF-related apoptosis-inducing ligand (TRAIL) will be co-functionalized on the flow chamber surface with selectins. Effects of these substrata exposures on stem cell proliferation, apoptosis, clonogenic outgrowth, and NOD-SCID reconstituting capacity will be measured. While these studies will be designed primarily to further understanding of how leukemic and normal hematopoietic stem cells interact with selectins and other endothelial substrata, they also have implications for other tumor types in terms of defining cell interactions with vascular substrata and for discovering means to exploit these interactions to enhance normal stem cell capture and survival and to optimize malignant stem cell destruction. PUBLIC HEALTH RELEVANCE: Understanding how the stem cells which give rise to leukemia interact with other cells and proteins in the marrow and in blood vessels has potential to aid in understanding how these malignant stem cells can be more effectively eliminated from patients who develop various types of myeloid and lymphoid leukemias. They also have implication for understanding of survival and proliferation of normal stem cells which would have impact on stem cell transplantation and implantation therapies.